Exercise programs and equipment are used by many people for a variety of purposes. Some people are interested in maintaining or improving body strength, and those persons may exercise with free weights or with exercise machines designed or programmed to develop particular parts of the body. Persons may also engage in various aerobic exercise activities designed to improve respiratory and circulatory functions by increasing oxygen consumption of the body. Examples of aerobic exercise include running, walking, and swimming, and many people use exercise machines or devices such as treadmills, stair climbers, and aerobic step exercisers, to perform aerobic exercises indoor or within a relatively closed space.
Generally speaking, the foregoing kinds of exercises and exercise equipment should be used by persons in good physical health who are working to maintain or improve their strength or stamina. However, exercise routines may also be important for those who, by reason of illness, infirmity, or age, require physical therapy as a remedial treatment of bodily disorder. For example, persons who have undergone cardiovascular surgery or who are recovering from a heart attack may have prescribed a regimen of relatively light exercises to aid their physical rehabilitation. Exercise machines such as stair climbers or treadmills, even used sparingly, may simply be too stressful for many such therapeutic applications of exercise. Moreover, such exercise machines may appear intimidating to elderly or very infirm patients, who would feel more comfortable with exercises conducted in a familiar or nonthreatening environment.